The Korea Composite Stock Price Index (KOSPI) opened sharply lower on Thursday after hotter US inflation data and AI doubts. South Korea’s benchmark then slid 7.28% to 5,571.27 by 10:13 a.m. Seoul time.

The drop extends a six-session losing streak and leaves the index roughly 40% below its June 19 peak. Even so, it remains up 31.87% for 2026, according to TradingView data.

What Pushed the KOSPI Into a Trading Halt?

US inflation, as measured by the Consumer Price Index (CPI), reached 3.7% in September, the Labor Department reported. Economists had expected 3.6%. Core inflation, which strips out food and energy, also beat forecasts at 2.6%.

Meanwhile, US stocks fell on Wednesday as inflation fears and AI skepticism weighed. The S&P 500 lost 1.11% and the Nasdaq Composite dropped 1.88%.

Korea JoongAng Daily reported the KOSPI opened 5.59% lower at 5,673.01, triggering a program trading pause at 9:08 a.m. The curb, called a sidecar, blocks automated sell orders from program trading for five minutes. It applies once KOSPI 200 futures fall 5% and stay there for a minute.

Samsung Electronics fell 6.03% and SK Hynix dropped 7.61% shortly after the open. In addition, foreign investors sold a net 285.6 billion won early in the session.

KOSPI opened down and is still falling. Source: Trading View

Both chipmakers were already under pressure from a memory chip advance by China’s ChangXin Memory Technologies.

Can Seoul Find Footing Before the Fed Meets?

The report revived fears of another Federal Reserve (Fed) rate hike at its October 27 and 28 meeting. The central bank already raised rates in September.

Therefore, higher rates would raise borrowing costs for companies funding AI data centers with debt. NVIDIA fell more than 3% on Wednesday.

Brent crude also trades near $106 a barrel as Middle East tensions persist.

Earlier this week, a broader Asian equity rout had already dragged on global risk appetite.

Thursday’s drop shows how one inflation surprise can ripple from Fed expectations to AI financing costs and Korean chipmakers. The Fed’s October 28 decision will show whether those pressures ease.

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